An enhanced state of protein modification due to increased in vivo production of various sugar-derived or lipid-derived carbonyl compounds via non-enzymatic biochemical reactions is called “carbonyl stress” (Miyata et al. Kidney Int. 55: 389–399, 1999; Miyata et al. J. Am. Soc. Nephrol. , 11:1744–1752,2000). These carbonyl compounds have been reported to be involved in adult diseases, such as diabetes mellitus and arteriosclerosis, as well as aging, via Maillard reaction. The Maillard reaction is a non-enzymatic glycation reaction between a reducing sugar, such as glucose, and amino acids or proteins. Maillard reported this reaction in 1912, focusing on a phenomenon of brown coloration arising upon heating a mixture consisting of amino acid and reducing sugar (Maillard, L. C., Compt. Rend. Soc. Biol., 72: 599, 1912). The Maillard reaction is involved in brown coloration, generation of aromatic components, taste, protein denaturation, and such reactions during heating or storage of foods. Therefore, this reaction has been mainly studied in the field of food chemistry.
However, in 1968, glycated hemoglobin (HbAlc), a micro fraction of hemoglobin, was identified in vivo and shown to increase in diabetic patients (Rahbar. S., Clin. Chim. Acta, 22: 296, 1968). These findings brought attention to the significance of in vivo Maillard reactions and the relationship between the reaction, the onset of adult diseases (such as diabetic complications and arteriosclerosis) and in progress of aging. For example, pyrraline and pentosidine, which are the late-stage products formed at post-Amadori compound formation reaction stages (advanced glycation end products; hereinafter abbreviated as AGE), are considered to serve as indices of aging and diabetes mellitus. In fact, highly reactive carbonyl compounds and AGE are accumulated at very high levels in the blood and tissues of chronic renal failure patients, regardless of the presence or absence of hyperglycemia (Miyata, T. et al., Kidney Int., 51: 1170–1181, 1997; Miyata, T. et al., J. Am. Soc. Nephrol., 7: 1198–1206, 1996; Miyata, T. et al., Kidney Int. 55: 389–399, 1999; Miyata, T. et al., J. Am. Soc. Nephrol. 9: 2349–2356, 1998). This accumulation is ascribed to as carbonyl stress in renal failure, where proteins are modified as a result of the Maillard reaction when carbonyl compounds derived from sugars and lipids react with amino groups (Miyata, T. et al., Kidney Int. 55: 389–399, 1999). Recently, the involvement of carbonyl stress in the onset and progress of dialysis amyloidosis and arteriosclerosis, which are complications of renal failure, has been reported (Miyata et al. J. Clin. Invest., 92: 1243–1252, 1993; Miyata et al. Proc. Natl. Acad. Sci. USA, 93, 2353–2358, 1996; Miyata et al. FEBS Lett., 437, 24–28, 1998; Miyata et al. FEBS Lett., 445, 202–206, 1999). Hence, the pathophysiological significance of carbonyl stress in renal failure is established.
Therefore, improving the carbonyl stress state via removal of in vivo-generated carbonyl compounds can result in the suppression of AGE formation that is associated with renal failure, reducing tissue damage and complications.
Furthermore, during peritoneal dialysis waste products are excreted from the blood across the peritoneum to the peritoneal dialysate. In blood of renal-failure patients, peritoneal dialysate with high osmotic pressure (dialysate containing glucose, icodextrin; amino acids, etc.) accumulate highly reactive carbonyl compounds via peritoneum into the peritoneal dialysate in peritoneal cavity. This results in an increase in the carbonyl compound concentration within the peritoneal dialysate, thereby causing a carbonyl stress state. As a result, the peritoneal function is lowered, due to the modification of intraperitoneal proteins with carbonyl; this reaction, in turn is presumed to be involved in the impairment of water-removing ability and ingravescence of peritoneal sclerosis (Miyata, T. et al., Kidney Int., 58:425–435, 2000; Inagi R., et al., FEBS Lett., 463:260–264, 1999; Ueda, Y., et al., Kidney Int. (in press); Combet, S., et al., J. Am. Soc. Nephrol., 11:717–728, 2000).
Indeed, immunohistochemical examinations of the endothelia and mesothelia have demonstrated that the intraperitoneal carbonyl stress state in peritoneal dialysis patients is induced by glucose contained in the peritoneal dialysate (Yamada, K. et al., Clin. Nephrol., 42: 354–361, 1994; Nakayama, M. et al., Kidney Int., 51: 182–186, 1997; Miyata, T. et al., Kidney Int., 58: 425–435, 2000; Inagi R., et al., FEBS Lett., 463: 260–264, 1999; Combet, S., et al., J. Am. Soc. Nephrol., 11: 717–728, 2000). Furthermore, the methylglyoxal contained in the peritoneal dialysate has been revealed to act on endothelial and mesothelial cells to enhance the production of vascular endothelial growth factor (VEGF), an agent presumed to play a central role in the impairment of peritoneal function (Combet et al. J. Am. Soc. Nephrol., 11: 717–728, 2000; Inagi et al. FEBS Let, 463: 260–264, 1999). Hence, carbonyl stress is also presumed to cause morphological changes in the peritoneum accompanied by functional (water-removing ability) impairment in dialysis patients. Therefore, a method to ameliorate the stress is required in the art.
Recently, the mechanism of the in vivo system to eliminate and metabolize carbonyl compounds has been revealed. A number of enzymes and enzyme pathways, such as aldose reductase, aldehyde dehydrogenase, and glyoxalase, have been reported to be involved in the elimination of carbonyl compounds. The decrease in the activities of these carbonyl compound-eliminating systems leads directly to a rise in the levels of many types of carbonyl compounds. Redox coenzymes, such as glutathione (GSH) and NAD(P)H, play important roles in such pathways (Thornalley P. J., Endocrinol Metab 3: 149–166, 1996). Carbonyl compounds, such as methylglyoxal and glyoxal, react non-enzymatically with thiol group of GSH and are eventually metabolized by glyoxalase. NAD(P)H activates glutathione reductase to increase the GSH level. Therefore, decrease of GSH and NAD(P)H by an imbalance in intracellular redox mechanisms blocks the carbonyl compound-elimination system and leads to the accumulation of AGE. In fact, blood GSH levels in patients with diabetes mellitus is reported to be reduced, whereas the levels of the carbonyl compound, methylglyoxal, in these patients are reported to be elevated.
As described above, a decrease in concentration of redox coenzymes, such as GSH and NAD(P), is suspected to be the cause of AGE formation because of a decreased elimination of carbonyl compounds. Thus, carbonyl stress was suggested to be relieved by elevating thiol level. Based on this theory, the present inventors tried to directly administer thiol compounds, such as GSH and cystein. In fact, incubation of sera from a normal person and patients with diabetes mellitus by adding these thiol compounds suppressed the production of AGE. However, a long period was required to gain such suppression, making this impractical.
Furthermore, AGE has been known to be generated through a carbonyl-amino chemical reaction between carbonyl compounds and proteins. Hence, it was concluded that carbonyl stress can be relieved with compounds that can chemically trap these products. Such compounds include hydrazine group-containing aminoguanidine (Brownlee M. et al., Science 232: 1629–1632, 1986), and 2-isopropylidenehydrazono-4-oxo-thiazolidin-5-ylacetanilide (Nakamura S. et al., Diabetes 46: 895–899, 1997). Beside these compounds, biguanides, such as metformin and buformin, can also trap carbonyl compounds. In vitro experiments demonstrated that all of these compounds efficiently trap carbonyl compounds, methylglyoxal and glyoxal (Miyata T., J. Am. Soc. Nephrol. 11: 1719–1725, 2000). However, in spite of the efficient inhibition of the production of AGE by these compounds, the specificity of these compounds to carbonyl compounds is low since they react with all types of carbonyl compounds. As a result, these compounds not only trap sugar-derived or lipid-derived carbonyl compounds that are deleterious to living cells, but they also trap carbonyl groups, such as pyridoxal, which are essential for living cells.
To solve the above problem, development of carbonyl stress-ameliorating agents, which can rapidly ameliorate carbonyl stress and are specific to sugar or lipid-derived deleterious carbonyl compounds, is desired in the art.
An in vivo system is known wherein one of deleterious carbonyl compounds, methylglyoxal, is converted to lactic acid. Methylglyoxal is converted to lactic acid in the glyoxal system that consists of GSH, glyoxal I, and glyoxal II. The glyoxalase I has also been known to act on other keto-aldehyde compounds besides methylglyoxal. However, the physiological role of this system remains to be understood. Furthermore, the use of this system for ameliorating carbonyl stress state in living cells has not been previously reported.